Various type of glow plugs have previously been proposed, one glow plug, for example, being described in German Patent Publication 1,526,775, (corresponding to British Pat. No. 1,127,454) which uses a spiral ribbon as the heating element. The spiral ribbon of this type of glow plug is exposed to the combustion gases and to the inside of the combustion space of the engine, and thus requires special material which can withstand the severe enviromental conditions pertaining within the combustion of an internal combustion engine, including the very high temperatures, exposure to corrosive gases, and the like.
Closed, protected glow plugs, for use in internal combustion engines have been proposed and are generally known and described in the literature - see German Patent 1,119,598 (corresponding to British Pat. No. 861,275) and U.S. Pat. No. 3,407,794, in which the latter is a glow plug which also includes a fuel supply thereto. A detailed description of the art of glow plugs is, thus, not necessary since these are structures which are well known.